The role of plasmid and host gene products in the replication of the pSC101 plasmid will be investigated. This plasmid is a member of a family which specify resistance to many antibiotics. Since they are frequently found in strains of pathogenic bacteria, understanding their replication is important for designing strategies to control their propagation in bacterial populations. The reason for choosing pSC101 as an object of study is that it is unique amongst bacterial plasmids in its requirement for the host dnaA protein for replication. This protein is essential for initiation of replication of the bacterial chromosome; and therefore, pSC101 also serves as a model system to study bacterial DNA replication. Mutations in plasmid functions that are required for replication will be isolated and characterized genetically and biochemically. The RNAs and proteins involved in replication will be identified and their interactions studied in vivo and in vitro to discover how pSC101 replicates and how this replication is regulated. Host gene products which interact with the plasmid replication proteins will be identified by suppressor analysis.